Pump

ABSTRACT

A rotary pump which includes a housing having inner and outer cylindrical surfaces defining a substantially annular internal pumping chamber. A substantially cup-shaped impeller, having inner and outer cylindrical surfaces, is movable within the chamber and is driven by an eccentric member connected to a rotary drive shaft. The position of the impeller is such that the outer housing surface and the inner impeller surface are simultaneously in substantially tangential engagement, respectively, with the outer impeller surface and the inner housing surface at diametrically opposite points of the impeller. The chamber is thereby divided into a pair of crescent-shaped compartments, the wide portion of each being proximal, respectively, to the diametrically opposite points. A flexible guide is fixed to the housing and engages the impeller within the chamber to constrain rotary movement. Inlet and outlet channels are formed in the housing on opposite sides, respectively, of the guide.

United States Patent Arnold 1 Feb. 29, 1972 [54} PUMP Primary ExaminerCarlton R. Croyle [72] inventor. Kurt Herbert Arnold, W. Caldwell, NJ. Assistant Examiner john j Vrablik [73] Assignee: Valcor Engineering Corporation, Kenil- Att0meyDarby & Darby worth, NJ. 57 AB T [22] Filed: June v1, 1970 STRAC A rotary pump which includes a housing having inner and [21] App! 41352 outer cylindrical surfaces defining a substantially annular internal pumping chamber. A substantially cup-shaped impeller, 52] us. Cl ..4l8/56, 418/59, F04c/l/02 having and W cylindrical Surfaceeis movable within [51] "FMC 1/02, F03: 3/00 the chamber and is driven by an eccentric member connected [58] Field of Search ..4 1 8/6, 56, 58,59, 209; a Mary drivfl Shaft Tile w the impeller is that 73/257 the outer housing surface and the inner impeller surface are simultaneously in substantially tangential engagement, respec- [56] References Cited tively, with the outer impeller surface and the inner housing surface at diametrically opposite points of the impeller. The UNITED STATES PATENTS chamber is thereby divided into a pair of crescent-shaped compartments, the wide portion of each being proximal, LZ29'676 6/1917 respectively, to the diametrically opposite points. A flexible 4/1933 guide is fixed to the housing and engages the impeller within 2 10/1958 the chamber to constrain rotary movement. lnlet and outlet 3494293 2/1970 channels are formed in the housing on opposite sides, respeclgx tively, of the guide. 3,463,091 8/1969 Delsuc ..418/59 14 Claims, 6 Drawing Figures 3 A H] \I T s-' i 34 l8 f T 37 39 22 2 \j t, 2

l7 l6 -5| l 52 PATENTEDreazs Ian 3.645.653

sum 1 [IF 2 FIG. 3

INVENTOR. KURT HERBERT ARNOLD ATTOR NE YS PAIENTEBFEBZQ I972 3. 645,653

sum 2 OF 2 INVENTOR. KURT HERBERT ARNOLD ATTORNEYS PUMP BACKGROUND OF THE. INVENTION The invention relates to a device for transporting fluids, and more particularly, to a rotary piston pump which is capable of providing negligible pulsation with one movable component.

I-Ieretofore, rotary pumps of the gyratory piston type have consisted of a relatively solid and substantially cylindrical piston which gyrates around the axis of a pump chamber having a slightly larger diameter. The radial spacing or displacement volume between the outer cylindrical face of the piston and the bore of the chamber constantly changes its location as the piston moves. Fluid which is drawn into this displacement volume through an inlet port is caused to move about the piston and is forced out through an outlet port proximal to the inlet port. These ports are separated from each other by a vane or partition which prevents the direct passage of fluid therebetween. The vane is usually connected to the piston and as the latter gyrates, the former slides in and out of a recess located between the inlet and outlet ports. Fluidtight contact between the vane and the sidewalls of the recess is desirable but generally impossible. Some leakage of fluid ordinarily occurs between the intake and discharge portions of the displacement volume in the region of the ports, thereby reducing the efficiency of'these prior pumps.

It has been found that prior arrangements frequently produce a substantially pulsating flow since the displacement volume is regularly reduced to zero in the area of the outlet port. Prior attempts to develop a pump capable of providing negligible pulsation have resulted in a double acting configuration which includes a pair of coaxial pistons mounted side by side in separate pumping chambers and operating approximately 180 out of phase. Such pumps have depended upon the use of packings and glands to seal the rotating drive shaft and have therefore given rise to potential contamination of the fluid transfer process. Furthermore, operational wear on the components have made periodic replacement of the packing material or seals, and the attending inconvenience, unavoidable.

According to the present invention, a substantially annular piston or impeller is made to revolve eccentrically around the axis of a substantially annular pumping chamber. The inner and outer cylindrical surfaces defining the pumping chamber are in simultaneous and substantially tangential engagement, respectively, with the inner and outer cylindrical surfaces of the impeller at diametrically opposite points, such that the pumping chamber is divided by the impeller into a pair of substantially crescent-shaped compartments displaced by approximately 180 operating degrees. Inlet and outlet channels are provided to communicate with each of these compartments so that a substantially nonpulsating flow results upon operation of the pump. The pumping chamber is partitioned between proximal portions of the inner and outer cylindrical boundaries thereof, to separate the inlet channels from the outlet channels and to prevent the direct passage of fluid therebetween. The partition may pass through an axial slot in the impeller and serve to constrain rotary movement of the latter. Movement of the impeller is effected by an eccentric member connected to a rotary drive shaft.

One object of the present invention is to provide a rotary pump having only one moving part which is capable of supplying a substantially nonpulsating flow.

Another object of the present invention is to provide a rotary pump in which the operating friction is minimized owing to a rolling contact between the operating components.

Still another object of the present invention is to provide a rotary pump which can be fabricated from a synthetic material, such as Teflon, having a low frictional coefficient.

A further object of the present invention is to provide a rotary fluid transport mechanism that is simple in construction and design.

BRIEF DESCRIPTION OF THE DRAWINGS For a further understanding of the present invention, reference may be had to the accompanying drawings, in which:

FIG. 1 is a vertical, cross-sectional view of a rotary pump constructed in accordance with the present invention;

FIG. 2 is a sectional view taken along the line 2--2 of FIG.

FIG. 3 is a sectional view taken along the line 3-3 of FIG.

FIG. 4 is a sectional view similar to FIG. 2 in which the piston has been moved from the position shown in FIG. 2;

FIG. 5 is a sectional view similar to FIG. 4 in which the piston has been moved from the position shown in FIG. 2; and

FIG. 6 is a sectional view similar to FIG. 2 of another embodiment of the present invention.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, and in particular to FIGS. 1 and 2, wherein there is illustrated a rotary pump, generally indicated by reference numeral 10, which includes a casing 11 having an internal, substantially nonuniform cylindrical bore 12, one portion of which is defined by a substantially cylindrical boundary surface 13. Bore 12 may be open at one end, and a cover plate 14 attachable to the casing at this open end may contain a substantially cylindrical promontory 16 which is coaxial with the bore 12. The diameter of the promontory 16 is substantially smaller than the diameter of the bore. The promontory has an axially extending cylindrical surface 17, and it, together with the surface 13, form the inner and outer boundaries, respectively, of a substantially annular internal cavity or pumping chamber 18. The promontory 16 may be internal with, or otherwise connected to the cover plate 14. It will be understood that the annular pumping chamber 18 may be formed in any convenient way, and that the present mode is not intended to limit the invention.

The present embodiment includes a fluid inlet port 19 which communicates with the pumping chamber 18. The port 19 may extend radially outward from the cylindrical surface 13 of the casing 11 to the external surface of the casing where it may be adapted by any convenient means for a fluid supply conduit to be attached thereto. Similarly, a fluid outlet port 21, which also communicates with the pumping chamber 18, may extend from a position proximal to the inlet port 19 radially outward through the casing 11 and may also be adapted for a fluid conduit to be attached thereto. It should be noted however, that the particular location of the fluid inlet and outlet ports is not critical or essential to the invention, and that they may also be positioned, for example, to communicate with the pumping chamber 18 from within the promontory 16.

A substantially annular or cup-shaped piston or impeller 22 is movably disposed within the pumping chamber 18. The outer diameter of the impeller 22 is substantially less than the diameter of the outer boundary surface 13 of the'pumping chamber, while the inner diameter of the impeller is substantially greater than the diameter of the inner boundary surface 17 The result is to divide the pumping chamber into a pair of compartments, or displacement volumes, 23 and 24, formed respectively between the impeller and the outer boundary surface 13, and between the impeller and the inner boundary surface 17.

A rotary drive shaft 26, driven in any suitable manner, is journaled within a radial end plate 27 of the casing 11. The end plate may contain an axially depending cup-shaped bearing shield 28 which is coaxial with the pumping chamber 18, and which contains a bearing 29. The shaft 26 is provided with an offset or eccentric portion 31 which is coaxial with the impeller 22. The cup-shaped impellerincludes a radial base portion 32 having an axial recess or bore, 33, into which a substantially cup-shaped bearing shield 34 may be nonrotatably 101 mu n11:

secured. The shield is proportioned snugly to receive a bearing 36 which engages the eccentric portion 31 of the drive shaft 26 to permit rotary movement thereof relative to the impeller 22. The bearing 36 may be the plain bearing illustrated in FIG. 1, or alternatively, it may be a ballbearing (not shown) having an inner race which is rigid with the eccentric portion 31 of the drive shaft 26 and an outer race which is a tight fit within the axial shield 34. It should be noted that the 31 may either be formed on or secured to the rotary shaft 26.

The axis of the impeller 22 is displaced from the axis of the rotary shaft 26 by an amount which equals the offset of the eccentric portion 31, and the outer radius of the impeller is less than the outer radius of the pumping chamber 18 by the same amount. The throw of the eccentric therefore serves to effect continuous engagement between the outer cylindrical boundary 13 of the pumping chamber 18 and the outer cylindrical surface 37 of the impeller. Similarly, the radius of the promontory 16 is less than the inner radius of the impeller by an amount equal to the amount of offset of the eccentric. The result is that the outer boundary surface 13 and the inner impeller surface 38 are simultaneously in substantially tangential engagement respectively with the outer impeller surface 37 and the inner boundary surface 17 at diametrically opposite points of the impeller. The compartments 23 and 24, therefore, are substantially crescent-shaped, the wide portion of each compartment being proximal respectively to the diametrically opposite points of contact between the impeller and the housing described above. The maximum width of each of these concentric chambers is equal to the throw of the eccentric 26.

A locater key or guide 39 preferably extends radially across the pumping chamber 18 from the promontory surface 17 to the outer cylindrical surface 13 of the casing 11, and is fixed to the latter at a point which is located between the fluid ports 19 and 21. The guide 39 also extends axially throughout the length of the pumping chamber 18, and it serves as a vane to prevent fluid entering through the inlet port 19 from flowing directly out the exhaust port 21 without first being subject to the action of the impeller 22. The impeller may contain an axial slot through which the guide passes to constrain rotary movement of the former upon operation of the pump, which will be more fully described below. It should be noted that the invention is not intended to be limited by the present configuration of the guide 39, and that other types of guides and partitions fixed to the housing and engaging the impeller may be suitable for present purposes.

A flexible sheath 41 which is formed from a generally fluidimpervious material, may be connected to, or integrally extending from the impeller 22 at points surrounding the axial recess 33. The outer end of the sheath is secured in fluidtight contact with the perimeter of the bore 12 in the casing 11. The sheath is substantially cylindrically shaped and surrounds the rotary drive shaft 26 and its bearings 29 and 36 to protect them from any fluid which may inadvertently escape from the pumping chamber 18 during operation of the pump. The sidewall portions of the sheath may be corrugated for at least a part of its length substantially to form a bellows for the purpose of flexing with movement of the impeller 22.

The casing 11 may be formed with a substantially annular projection 42, extending radially inwardly of the bore 12 and having an inner radial surface 43 which is disposed, upon operation of the pump, for continuous sliding engagement with the confronting surface portion of the radial base 32 of the impeller. As may be seen from FIG. 1, the inner lateral surface area of the impeller is simultaneously in continuous sliding engagement with the outer lateral surface area of the promontory 16. The result is that each of the pumping compartments 23 and 24 is substantially fluidtight. Any fluid which leaks from the outer pumping compartment 23 and into the region surrounding the fluid-impervious sheath 41 will be contained harmlessly out of contact with the driving mechanism of the pump. Conventional means, such as a relief port through the wall of the casing 11, may be provided for the discharge offluid which collects in the region of the sheath 41, so that there will not be a buildup of pressure to inhibit the operation of the pump.

As has been mentioned above, one object of the present invention is to provide a rotary pump capable of supplying a nonpulsating flow. Accordingly, the pumping compartments 23 and 24 are approximately 180 out of phase so that when the displacement volume of each compartment regularly reaches zero in the region of the ports, the instantaneous displacement volume of the other is a maximum. For example, it may be seen from FIG. 2, that the displacement volume 23 is a minimum with respect to the inlet and outlet ports 19 and 21, while the displacement volume 24 is a maximum. This circumstance contributes to a nonpulsating flow since each displacement volume in turn may be operative when the other is exhausted. In the present embodiment, fluid transfer between the inner displacement volume 24 and the inlet and outlet ports 19 and 21 is accomplished, respectively, by openings 44 and 46 in the wall of the impeller 22. It is preferable that these openings be located substantially adjacent to the guide 39, and separated thereby, so that they may communicate directly with the respective ports 19 and 21.

FIG. 3 illustrates the preferred configuration for the transfer openings 44 and 46. They may be formed, for example, between parallel fingers 47 forming part of the impeller 22 and extending longitudinally toward the guide 39. It will be understood, however, that the particular configuration of the openings 44 and 46 is not intended to limit the invention, and that for the present embodiment any suitable arrangement allowing fluid to transfer from one displacement volume to the otherin the region of the ports 19 and 21 would be acceptable.

The operation of the pump is illustrated in successive stages by FIGS. 1, 2, 4 and 5. It may be seen that as the drive shaft 26 rotates in ,the direction indicated by the arrow in FIG. 1, the eccentric portion 31 is rotated, and the rotary movement of the eccentric is transmitted through the bearing 36 to the impeller 22. However, rotary movement of the impeller is constrained by the guide 39, with the result that the former revolves, without rotating, about the axis of the pumping chamber 18.

As the impeller revolves, it moves back and forth in sliding engagement with the fixed guide 39 which may preferably be formed from a flexible or resilient material to absorb stresses resulting from the gyratory movement.

The radial spacing between the outer cylindrical surface 37 of the impeller and the outer cylindrical boundary 13, provides a displacement volume that constantly changes its location, in the manner common to rotary piston pumps as the shaft 26 is rotated. Fluid enters this displacement volume through the inlet port 19, and is caused to move about the impeller and is forced out through the outlet port 21. The guide 39 prevents a direct passage between the ports. The pumping compartment 24 is defined by the radial spacing between the inner cylindrical surface 38 of the impeller and the boundary 17 of the promontory 16. As the impeller revolves, this internal radial spacing provides an inner displacement volume that constantly changes its location simultaneously with the outer displacement volume, although it lags behind the latter by approximately 180 operating degrees. In FIG. 2, for example, the position of the impeller 22 is such that a portion of the pumping compartment 24 is open to receive fluid from the inlet port 19 through the opening 44, while access to the compartment 23 is effectively closed off. At the same time a discharge may occur exclusively from the compartment 24 through the opening 46 to the outlet port 21. In H6. 4, the impeller has moved approximately operating degrees from the position illustrated in FIG. 2. Fluid entering through the inlet port 19, and the opening 44, has substantially filled the inner compartment 24 on the intake side of the guide 39, and has only partly refilled the outer compartment 23 which is simultaneously discharging through the outlet port 21. While discharge of the inner compartment is nearly complete, it is important to note that substantially all of the discharge portion of the outer compartment remains.

In FIG. 5, the impeller has moved 180 operating degrees from the position illustrated in FIG. 2. In this position the inner compartment is satiated, neither receiving nor expelling fluid, while the outer compartment is simultaneously operative in both respects. At any moment during operation of the pump, therefore, one of the pumping compartments is either receiving or discharging fluid or is involved in both of these activities, so that the output from the pump is continuous.

It should be noted that a truly non-pulsating flow may occur only when there is substantial parity between the respective displacement volumes of the pumping compartments 23 and 24. In the present embodiment, the average diameter of the outer compartment 23 is greater than the average diameter of the inner compartment 24, and since the maximum width dimensions are equal, as has been described above, it is necessary to provide for unequal depth dimensions to achieve substantial displacement equivalency. Accordingly, the impeller 22 may be formed with an enlarged diameter base portion 48, (FIG. 1). This portion provides a shoulder or radially extending surface 49 which is disposed for sliding engagement relative to a confronting inner surface 51 of a radially directed recess 52'formed in the casing 11 at the base of the pumping chamber 18. The surface 49 of the base portion 48 may be slightly larger than the maximum radial distance between the outer cylindrical surface 37 of the impeller and the outer cylindrical boundary 13, so that surface 49 forms the effective base of the outer pumping compartment 23. It may be seen from FIG. 1, therefore, that the axial length of the outer compartment 23 is substantially less than that of the inner compartment 24. This difference may be calculated in a known way so that the respective volumes are equal. However, the invention is not intended to be limited by this particular configuration, and there is illustrated only one convenient way to establish parity between the respective displacements of compartments 23 and 24.

In the embodiment of the invention that is illustrated in FIG. 6, the pump is constructed in a manner similar to the pump that is shown in FIGS. 1-5, and accordingly, only those parts that are different will be describe in detail.

One essential characteristic of the present invention is that access be provided for fluid to enter and exit from the inner compartment 24. Accordingly, a supplementary inlet port 144 may be provided in the promontory 16 to communicate directly with the compartment 24 on one side of the guide 39, so that fluid may be supplied internally of the impeller 22. Likewise, a supplementary outlet port 146 may be provided in the promontory 16 on the other side of the guide 39. Such a configuration renders transfer passages or openings in the impeller 22 unnecessary.

The operation of the present embodiment is substantially the same as that of the pump illustrated in FIGS. 1-5. Fluid enters the intake portions of the compartments 23 and 24, respectively, through inlet ports 19 and 144. As the impeller 22 revolves, the inner and outer displacement volumes continuously change position until fluid begins to exit first through outlet port 21 and subsequently through outlet port 146 so that the flow produced by the pump is substantially nonpulsating. As has been mentioned above, the guide 39 prevents the direct passage of fluid between the inlet and outlet ports, and while some leakage may occur from one chamber to the other in the area of sliding contact between the impeller and the guide, the amount is usually minor and has no substantial effect upon the efficiency of the pump.

The working parts of the pump preferably are formed from a chemically inert material such as Teflon" to enable the pump to circulate a large variety of fluids such as acids and other chemicals, resins, slurries, preservatives, biologicals, soaps, oils, glue and wax. The gyrational movement of the impeller 22 serves to reduce operational friction, since the impeller is in substantially rolling contact with the housing surfaces defining the pumping cavity. The use of Teflon" further serves to minimize friction and consequent wear on the components.

What is claimed is:

l. A rotary pump, comprising:

a housing, having inner and outer wall surfaces defining a substantially annular internal cavity;

a substantially annular impeller movable within said cavity and having inner and outer cylindrical surfaces, said outer housing surface and said inner impeller surface being simultaneously in substantially tangential engagement, respectively with said outer impeller surface and said inner housing surface at diametrically opposite points of said impeller to divide said cavity into inner andouter crescent-shaped chambers, the wide portion of each of said chambers being proximal respectively to said diametrically opposite points;

a plurality of channels formed in said housing and communicating with said cavity;

means for revolving said impeller eccentrically within said cavity;

guide means connected to said housing for constraining rotary movement of said impeller; and

a substantially annular sealing member adapted for movement conjointly with said impeller and extending radially between said outer impeller and outer housing surfaces, the upper extremity of said member defining one end wall of said outer chamber, said inner chamber extending to a point below said upper extremity such that the displacement volume of said outer chamber is substantially the same as the displacement volume of said inner chamber.

2. The rotary device, as recited in claim 1, wherein said revolving means comprises a rotary drive shaft having a por tion offset from the axis of said shaft and engageable with said impeller, the radius of said outer impeller surface being less that the radius of said outer housing surface by an amount equal to the amount of said offset.

3. The rotary pump, as recited in claim 1, wherein said impeller is substantially cup-shaped.

4. The rotary pump, as recited in claim 1, wherein said guide means comprises a substantially radially projecting member extending from at least one of said inner and outer cylindrical housing surfaces and contacting said impeller to prevent rotation thereof within said cavity.

5. The rotary pump, as recited in claim 4, wherein said radially projecting member engages said inner and outer cylindrical housing surfaces.

6. The rotary pump, as recited in claim 5, wherein said member comprises a substantially flexible partition which extends axially along the length of said cavity, said impeller having a substantially axial slot through which said member passes.

7. The rotary pump, as recited in claim 6, wherein said member is substantially resilient.

8. The rotary pump, as recited in claim 1, wherein said plurality of channels comprises first and second ports, said first port communicating with said cavity on one side of said guide means, and said second port communicating with said cavity on the other side of said guide means.

9. The rotary pump, as recited in claim 8, wherein each of said first and second ports communicates with said first chamber.

10. The device of claim 9, wherein said impeller comprises first and second transfer passages connecting said first and second chambers, said passages being proximal respectively to said ports.

11. The rotary pump, as recited in claim 1, wherein said plurality of channels comprises first and second inlet ports communicating with said cavity on one side of said guide means, and first and second outlet ports communicating with said cavity on the other side of said guide means.

12. The rotary pump, as recited in claim 11, wherein said first inlet port and said first outlet port communicate with said first chamber, and said second inlet port and said second outlet port communicate with said second chamber.

Home 011:

13. The rotary pump of claim 1 wherein said sealing member comprises a radially protruding flange formed as part of said impeller.

14. The rotary pump of claim 13 wherein said outer housing surface comprises an annular recess extending radially outwardly from said cavity, and said flange extends into said recess for sliding engagement therewith. 

1. A rotary pump, comprising: a housing, having inner and outer wall surfaces defining a substantially annular internal cavity; a substantially annular impeller movable within said cavity and having inner and outer cylindrical surfaces, said outer housing surface and said inner impeller surface being simultaneously in substantially tangential engagement, respectively with said outer impeller surface and said inner housing surface at diametrically opposite points of said impeller to divide said cavity into inner and outer crescent-shaped chambers, the wide portion of each of said chambers being proximal respectively to said diametrically opposite points; a plurality of channels formed in said housing and communicating with said cavity; means for revolving said impeller eccentrically within said cavity; guide means connected to said housing for constraining rotary movement of said impeller; and a substantially annular sealing member adapted for movement conjointly with said impeller and extending radially between said outer impeller and outer housing surfaces, the upper extremity of said member defining one end wall of said outer chamber, said inner chamber extending to a point below said upper extremity such that the displacement volume of said outer chamber is substantially the same as the displacement volume of said inner chamber.
 2. The rotary device, as recited in claim 1, wherein saId revolving means comprises a rotary drive shaft having a portion offset from the axis of said shaft and engageable with said impeller, the radius of said outer impeller surface being less that the radius of said outer housing surface by an amount equal to the amount of said offset.
 3. The rotary pump, as recited in claim 1, wherein said impeller is substantially cup-shaped.
 4. The rotary pump, as recited in claim 1, wherein said guide means comprises a substantially radially projecting member extending from at least one of said inner and outer cylindrical housing surfaces and contacting said impeller to prevent rotation thereof within said cavity.
 5. The rotary pump, as recited in claim 4, wherein said radially projecting member engages said inner and outer cylindrical housing surfaces.
 6. The rotary pump, as recited in claim 5, wherein said member comprises a substantially flexible partition which extends axially along the length of said cavity, said impeller having a substantially axial slot through which said member passes.
 7. The rotary pump, as recited in claim 6, wherein said member is substantially resilient.
 8. The rotary pump, as recited in claim 1, wherein said plurality of channels comprises first and second ports, said first port communicating with said cavity on one side of said guide means, and said second port communicating with said cavity on the other side of said guide means.
 9. The rotary pump, as recited in claim 8, wherein each of said first and second ports communicates with said first chamber.
 10. The device of claim 9, wherein said impeller comprises first and second transfer passages connecting said first and second chambers, said passages being proximal respectively to said ports.
 11. The rotary pump, as recited in claim 1, wherein said plurality of channels comprises first and second inlet ports communicating with said cavity on one side of said guide means, and first and second outlet ports communicating with said cavity on the other side of said guide means.
 12. The rotary pump, as recited in claim 11, wherein said first inlet port and said first outlet port communicate with said first chamber, and said second inlet port and said second outlet port communicate with said second chamber.
 13. The rotary pump of claim 1 wherein said sealing member comprises a radially protruding flange formed as part of said impeller.
 14. The rotary pump of claim 13 wherein said outer housing surface comprises an annular recess extending radially outwardly from said cavity, and said flange extends into said recess for sliding engagement therewith. 